Boev, Zlatozar, and Heimo Mikkola. “First Pleistocene Record of Great Grey Owl (Strix Nebulosa Forster, 1772) in Bulgaria”. Proceedings of the Bulgarian Academy of Sciences 75, no. 5 (May 31, 2022): 680–685. Accessed May 17, 2026. https://www.proceedings.bas.bg/index.php/cr/article/view/80.